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    <title>Document</title>
    <style>
        .box1 {
            width: 100px;
            height: 100px;
            background-color: red;
        }

        .box2 {
            width: 200px;
            height: 200px;
            background-color: green;
        }
    </style>
</head>

<body>
    <div id="div">
        <!--  <div :class="{box1:true,box2:flase}">  -->
        <div :class="{box1:flase,box2:true}">
            55
        </div>

        <!-- <div :class="[box1,box2]">  -->
        <div :class="['box2']">
            66
        </div>
    </div>
</body>
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<script>
    const app = new Vue({
        el: '#div',
        data: {

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